Synthetic lubricants



ite grates 3,065,180 Patented Nov. 20, 1962 This invention relates tosynthetic lubricants.

Synthetic lubricants have previously been proposed consisting of a blendof a liquid aliphatic diester of a saturated aliphatic dicarboxylic acidand a polyester of the general formula:

H(R *OOCR COO) R OI-I (I) ere R is the hydrocarbon radical of analiphatic diarboxylic acid, R is the hydrocarbon radical of a glycol andn is a number from 1-10 (see UK. patent specification 763,077).

We have now found that certain blends of the above type, or similar tothe above type, can be produced that have properties which render themparticularly suitable for aero gas turbine lubrication.

According to the invention, a lubricating composition comprises a blendof a liquid aliphatic diester of a sat rated aliphatic dicarboxylicacid, and a polyester, soluble in the diester, and having the generalformula:

where:

n is an integer,

The R s are methyl or ethyl groups, preferably methyl groups,

The R s are alkyl groups having 1-4 carbon atoms, preferably methyl orpropyl groups, and

The R s are alkylene groups having 4-.14, preferably 6-10 carbon atoms,

the relative proportions of diester and polyester in the blend beingsuch that the viscosity of the blend at 210 F is 4-30, especially 410,particularly 6-10, centistokes.

Preferred diesters for use in the blends according to the invention arethose of the formula:

where R is an alkylene group having 4-14 carbon atoms and the R s arealkyl groups, preferably branched chain having 4-18 carbon atoms.

Examples of suitable diesters are:

(a) Di(2-ethylhexyl) sebacate (di-octyl sebacate).

(b) Di(3:5:5-trimethy1hexyl) sebacate (di-nonyl sebacate).

(c) Z-ethylhexyl (3:5 :S-trimethylhexyl) sebacate (octyl nonylsebacate).

(d) Arnixture of (a), (b) and (0).

Preferred polyesters are those of Formula H having a viscosity at 25 C.of at least 50, especially at least 500, centistokes, particularly thosein which the R s have 7 or 8 carbon atoms, especially octamethylene,l-ethylhexamethylene, 1 :4-diethyltetramethylene, 1:1:3-trimethyltetramethylene or 1 :3 3-trin1ethyltetramethylene.

It is to be understood that different R groups, different R groups anddifferent R groups may be present in any given polyester molecule, thatdifferent R4, groups may be present in any given diester molecule andthat mixtures of different polyester molecules and/or different diestermolecules may be present in the same blend.

Polyesters for use in the lubricant blend according to the invention maybe prepared by reacting in one or more stages, the followingingredients:

(a) An acid or acids of the formula HOOCR COOH,

and (b) A diol or diols of the formula HOCH C(R (R CH OH Where R R and Rhave the values given previously, the molecular portion of diol(s) beinggreater than, but preferably not more than twice, the molecularproportion of acid(s). As stated above, mixtures of polyesters ofFormula I may be used in the lubricant blend i.e. polyesters havingdifferent values of n and having different acid and diol residues. Withsuch a mixture, the average value of 11 would not necessarily of coursebe a whole number. Thus when preparing a polyester mixture, themolecular proportions of the ingredients to be reacted need not bepresent in whole number ratios.

Examples of acids which may be used in the preparation of the polyesterare adipic acid, azelaic acid, brassylic acid, suberic acid and pimelicacid.

Particularly satisfactory acids have been found to be:

(a) Sebacic acid,

('b) Commercial iso-sebacic acid which consists essentially of 2-ethylsuberic acid (7280% 'wt.), 2:5-diethyladipic acid (12-18% wt.) andsebacic acid (640% wt.), and

(c) M equimolecular mixture of 2:2:4-trimethyl adipic acid,2:4:4-trimethyladipic acid and sebacic acid.

The most satisfactory diols have been found to be:

(a) 2:2-dimethyl-1:3-propanediol (neopentyl glycol), and (b)2-methyl-2-propyl-1:3-propanediol (available commercially under thetrade name Mepropol).

Preferably the blend according to the invention is one containing 5-60%by weight of polyester, especially 535%, the remainder of the blendbeing substantially diester.

Any antioxidant for lubricants, for example phenothiazine, may beincorporated in the blend if desired.

Polyesters P21, P27, P221, P222, P223 and P226 were prepared from theingredients listed in Table I below by the following method:

The ingredients were reacted in a three-necked flask fitted with astirrer, a nitrogen inlet tube and a water-cooled, downward facingcondenser fitted with a Dean and Stark water trap. The water was removedfrom the trap at such a rate that the diol/Water interface remainedstatic at the top of the trap thus ensuring that the diol in thedistillate was automatically returned to the reaction vessel. A nitrogenflow rate of 6 litres/hour was used and the following heating cycle wascarried out:

Heat to 200 C. over 8 hours.

Maintain at 200 C. for 40 hours.

Maintain at 200 C. at 1 mm. of mercury pressure until an acid value of 1mg. KOH/g. was obtained.

Table I gives the composition and properties of polyesters P21, P27,P221, P222, P223 and P226.

Table I Molecular proportions Polyester Viscosity at C.

Commer- 2:2:4tri- 2 4:4-tr1- Sebacic Neopcntyl cial isomethyl methylacid glycol Mepropol sebacic acid adipic acid adipic acid 50, 520 cp.Immobile. Insufiicient sample. 90,000 cs.

Nora-cs. centistokes, cp. centipoises.

These polyesters were blended with a diester and phenothiazine to formblends B21, B27, B221, B222, B223 and after heating for 2, 3, 4 and 5hours and the viscosity at 100 F. measured.

Table 11 Ingredients of blends: Low temperature performance Thermalpercent weight stability Viscosity Viscosity (open beaker Blend at 210F., at 100 F, test): Max.

centistokes centistokes Viscosity change in Diester Poly- Phenoat F.,Supercoolmg test viscosity at ester thiazine oentistokes 100 F., percent(P21 B27 86.29 12.71 1.0 7. 90 37. 98 8,888 Immobile but clear after 162hours at +4.2

(P27) -70 O. Mobile again by 54 C. B221.. 80.06 .94 1.0 7.8 37 10,000Immobile but clear after 00 hours at +4.2

(P221) 70 O. Mobile again by -58 C. B222... 90. 43 8.57 1. 0 7. 8 36. 57, 670 Immobile and opalescent after 136 hours -12. 1

(P222) at C. Mobile and clear again by -55 B223. 84. 26 14. 74 1.0 7.8237. 80 11,345 Clear after 06 hours at -70 C and (P223) mobile again by67 C. B226 87.23 11.77 1.0 7.7 36.2 9, 450 Immobile but clear after 162hours at 1.2

(P226) -70 O. Mobile again at -54 C. B61 91. 46 54) 1. 0 6. 50 28.30Immobile 20.2

P61 X 7.51 35.85 Immobile +13. 0

1 After prechilling at 65 F. for 12 hrs.

B226 having the compositions and properties shown in We claim:

Table II. The diester was prepared from equimolecular amounts of sebacicacid, Z-ethylhexyl alcohol and 325:5- trimethylhexyl alcohol. Inaddition to octyl nonyl sebacate, the, product also contained di-octyland di-nonyl sebacates. By way of comparison, certain properties arealso given of a commercially available synthetic aero gas turbinelubricant (X) and of a blend (B61) containing a known polyester ofFormula I (P61) which consists of a poly (propylene sebacate) availablecommercially under the trade name Reoplex 100.

It will be seen that the blends according to the invention (B21, B27,B221, B222, B223 and E226) have greatly improved thermal stabilitycompared with blend B61. (Thermal stability is indicated by a low changein viscosity after the high temperature treatment.) Furthermore, blendsB21, B27, B221, B222, B223 and E226 show excellent low temperatureproperties whereas blends B61 and X give poor performances at lowtemperatures.

The low temperature properties of blends according to the invention maybe further improved if desired by the addition of a crystallisationsuppressant, e.g. a polymerised alkyl ester of acrylic or methacrylicacid, but it is an advantage when good low temperature properties can beachieved without the addition of such materials since they appear tohave an adverse efiect on both the thermhal stability and shearstability of blends containing t em.

'The Open Beaker Test referred to in Table II was carried out asfollows: 250 ml. of oil were heated in a 400 ml. beaker in an ovenmaintained at an air temperature at 300 C. Samples of the oil werewithdrawn l. A lubricating composition consisting essentially of a blendof at least 1 diester selected from the group consisting ofdi(2-.ethylhexyl) sebacate, di(3:5:S-trimethylhexyl) sebacate and2-ethylhexyl (3:5 :S-trimethylhexyl) sebacate, and a polyester, solublein the diester, having the general formula HO CH2C(CH::) 2CH2OOCR1COOnCHQC (CH3) eCHzOH reacting an acid of the formula HOOCR COOH, where Ris an alkylene group having 7-8 carbon atoms, with a diol of the formulaHOCH C(CH CH OH, the mo lecular proportion of diol being greater thanbut not more than twice the molecular proportion of acid, the amount ofpolyester in the composition being 535% by weight, the viscosity of thepolyester at 25 C. being at least 500 centistokes and the relativeproportions of diester and polyester in the blend being such that theviscosity of the blend at 210 F. is 610 centistokes.

2. A lubricating composition according to claim 1, in which thepolyester is one in which the R s are radicals selected from the groupconsisting of octamethylene, l-ethylhexamethylene,1-4-diethyltetramethylene, 1:1-3- trimethyltetramethylene and l :3:3-trimethyltetramethylone.

3. A lubricating composition, according. to claim 1, containing inaddition a minor amount of phenothiazine as an antioxidant.

(References on following page) where n is an integer, and which has beenprepared by References Cited in the file of this patent UNITED STATESPATENTS Beavers et a1 Mar. 7, 1950 Sanderson Feb. 17, 1953 Buckmann Jan.3, 1956 Bell et a1. July 2, 1957 Blake et a1. June 2, 1959 Young et a1Mar. 22, 1-960 6 FOREIGN PATENTS 763,077 Great Britain Dec. 5, 1956OTHER REFERENCES Barnes et al.: Lubrication Eng, August 1957, pages454-458.

1. A LUBRICATING COMPOSITION ESSENTIALLY OF A BLEND OF AT LEAST 1DIESTER SELECTED FROM THE GROUP CONSISTING OF DI-(2ETHYLHEXYL) SEBACATE,DI-(3:5:5-TRIMETHYLHEXYL) SEBATE AND 2-ETHYLHEX (3:5:5-TRIMETHYLHEXYLSEBACATE, AND A POLYESTER, SOLUBLE IN THE DIESTER, HAVING THE GENERALFORMULA